Field of Invention
The present invention relates to a micro-electro-mechanical device, especially a micro-electro-mechanical device which includes a plurality of ribs on (or under) a diaphragm for improving the flatness of the diaphragm, to provide a better acoustic pressure sensing capability.
Description of Related Art
Because of small size, high sensitivity, and low power consumption, micro-electro-mechanical devices are commonly used in daily life applications such as game joystick, automobile control system, and electronic products. FIG. 1 shows a cross-section view of a prior art micro-electro-mechanical device 10. The micro-electro-mechanical device 10 is for example a capacitive micro-electro-mechanical microphone which includes a substrate 11, an electrode 12, a spacer 13, and a diaphragm 14 which vibrates in response to an external acoustic pressure. The diaphragm 14 and the electrode 12 are arranged in parallel to form a capacitor whose capacitance changes according to the vibration of the diaphragm 14, so that the volume and frequency of the received sound can be sensed and determined. However, in manufacturing the micro-electro-mechanical device 10, the manufacturing steps such as deposition, sputter, baking an annealing will cause the micro-electro-mechanical device 10 to suffer great temperature variations which easily cause the diaphragm 14 to warp due to stress release. In addition, in order to improve sensing sensitivity, the diaphragm 14 preferably has a large area and thin thickness to enhance the signal output; however, this will cause more severe warpage problem. The warpage will increase the stiffness of the diaphragm 14 to affect the frequency response and weaken the vibration capability of the diaphragm 14.
Therefore, it is desired to reduce the warpage so that the diaphragm is more responsive to acoustic pressure.